The economic performance of real estate investment trusts, or REITS, has a growing influence on millions of acres of U.S. forestland.

REITs gained control of about 15 million acres of timber in the U.S. after expanding by more than 20 percent annually between the mid-1980s and the mid-2000s, according to a report by Dovetail Partners, a nonprofit group that studies forest issues.

Apart from timber lands, REITs own shopping malls, apartment buildings, industrial areas, office parks and other real estate, according to the National Association of Real Estate Investment Trusts.

The structure of REITs was created by Congress in 1960 as a way to allow more people to invest in large real estate transactions, similar to how stockholders own shares in major corporations, according to the association.

The value of REITs soared during the real estate boom, more than doubling from about $140.5 billion in 1997 to $312 billion in 2007, according to the association's data.

The trusts suffered as a result of the housing bust, with their collective value plummeting nearly 40 percent in 2008, to less than $192 billion.

The structure of REITs as investment vehicles -- rather than traditional integrated wood products companies -- has sparked worries about the implications for forestlands.

According to Dovetail Partners, the "jury is still out as to the long-term impact of this ownership shift on forest management activities," but land conversion is a major concern.

Roughly 1 million acres of U.S. forests a year have been converted to non-timber uses since the 1990s, according to the U.S. Forest Service.

As part of their real estate operations, REITs sell land for development as well as conservation.

For example, a planned Plum Creek Co. project in Maine would involve the development of about 17,000 acres and the sale of about 29,000 acres to a conservation group.

Real estate sales constituted about 40 percent of the firm's $1 billion in total revenues so far this year, according to SEC filings.

Brooks Mendell, a financial analyst who tracks the timber industry, said massive conversion of forest acreage owned by REITs is unlikely. The prospect of finding such high numbers of willing buyers in a relatively short period of time is unrealistic.

"That story gets overblown," Mendell said. "They don't play out from an economic angle. Those are not realistic scenarios."

-- Mateusz Perkowski